Warning!! CHKDSK reduces your disk space. But it’s for your good

Microsoft’s hard disk scanning and repair utility, CHKDSK (“check disk”) may not be unfamiliar to a common Windows user. It’s been in Windows for more than 2 decades. Even on Microsoft’s latest OS - Windows 10, this utility is available in both command line format and graphical format.

Running CHKDSK in Windows 10 is very simple. Just assure that you have administrative privileges for that. Sometimes, the check disk process may take a long time – particularly, when you have a larger hard disk drive.

But today, let's not discuss “how to” questions. Instead, I’m thinking of addressing an issue – encountered by several users after running CHKDSK. Most of them have reported:

After running CHKDSK command, my hard disk space was found to be reduced to a considerable extent.

Probably, the first logical answer that comes to your mind when you read this issue is - it happened due to a bad command. But that's not entirely true.

Windows users can also make use of the Disk Management tool to save space on the hard disk.

Allow me to dig deep into the topic

Basically, CHKDSK is a file system integrity verifier. It fixes logical file system errors and marks bad sectors on the disk surface. The whole CHKDSK activity can be divided into 5 phases where 4th and 5th phases are optional.

1st phase (Check for Consistency): Here, CHKDSK examines each and every file record segment of a volume to its Master File Table (MFT) for internal consistency.

2nd Phase (Checking Indexes): In this phase, CHKDSK checks each directory on the volume and verify that every file or subdirectory referenced in a directory exists as a valid file record in the MFT. It also checks for circular directory references.

3rd Phase (Checking Security Descriptors): Here, CHKDSK verifies security descriptor associated with files/directories. These descriptors contain information about the ownership of file/directory, file permissions, etc.

4th & 5th Phases (Checking Sectors – Optional): If a user wants, he/she can go with this additional step. Here in the 4th phase, CHKDSK verifies the clusters in use. In the 5th phase, CHKDSK verifies cluster currently not in use. These phases may consume more time depending on the size of the drive.

Now, you’d got some idea on the topic. So, it’s easy for me to explain the real cause of the problem.

Checking sectors using CHKDSK is an optional phase in the process. People who have noticed a reduction in their disk spaces after CHKDSK might have chosen this option to check bad sectors on the drive. What eventually happened would be – more number of bad sectors are marked and blocked by CHKDSK. As the number of bad sectors increases, a user can see a significant reduction on his/her hard disk space.

The increase in the number of these bad sectors could be a serious problem as it indicates the possible failure of a hard drive. With CHKDSK, you can either skip scanning for bad sectors or try to recover data from those sectors. But, there’s an undeniable fact – some data may be corrupted. So, it’s always good to take backup of your important data rather blaming this utility.


Sectors of a hard drive may become bad/defective due to a number of reasons – especially aging. CHKDSK is a utility that alerts you the need to take care of your valuable files by mapping bad sectors on a drive. Also, this utility attempts to recover data from those defective sectors up to an extent. So, trusting this utility won’t cause any harm, actually it's a good sign that you got to know about your hard drive's health.

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John Harris

Senior Editor, Content Analyst and a fan of exceptional customer service. John develops and publishes instructional and informational content regarding partition management, Windows hot-fixes, data management and computer troubleshooting.

As a tenured data recovery specialist, John shares exceptional insights and blog posts about data loss and data recovery across any storage device. With 8+ years’ experience in writing for Data Recovery for both Mac OS and Windows OS computers, he is an avid learner who always wants to polish and simplify the data recovery process. John passes his free time playing Chess and reading Science Fiction novels.

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